Sea
water temps can be high in the South Seas. How will this effect
your engine cooling?

Dan
Streech responds:

The
keel cooler on the N40 is supplied by the Walter keel cooler
company of Jersey City, NJ. The sizing of the keel cooler
is a team effort between PAE, Walter and Alaska Diesel (Lugger)
and is based on the known heat rejection data of the engine
at various loads, ambient water temperature and boat speed
(water flow over the cooler).

We
at PAE consider worst case scenarios when sizing the cooler
on a new design. Our criteria for sizing the cooler are:
Seawater temperature: 85 F
Maximum heat rejection (meaning engine running at the full
power output)
Boat speed: 6 knots

In
actuality, the engine only requires about 35% of it's rated
power to move the fully loaded boat at 6 knots, so there is
quite a bit of reserve cooling available as the boat moves
into the warmer waters. From previous experience, I have been
aboard Nordhavns operating at normal cruising speeds in water
temperatures exceeding 90 degrees without any rise in the
coolant temperatures.

Since
the engine coolant temperature is thermostatically controlled
to 185 degrees, the gauge reading remains constant unless
the conditions overpower the keel cooler - which has never
happened.

The
ATW project has many purposes and one of them is to thoroughly
test our designs, concepts and assumptions. We may find some
unusual combination of events (such as towing an Arab dhow
in the Red Sea at 3 knots requiring full power in 95 degree
water) which causes an overheating of the engine. This would
tell us that future boats should have a larger cooler or avoid
the above mentioned practice.

As
an aside to your question, I will also mention that we are
testing a new device on the ATW boat. It is keel cooler dedicated
to the cooling of the hydraulic oil from the Naiad stabilizer
system. Since our dry exhaust/keel cooled boats don't use
any pumped raw sea water, the standard cooling system provided
by Naiad is only usable if we install a special 12VDC pump
dedicated to the cooling of the stabilizers. In our typical
installation, the pump is activated by a relay when the engine
is started. It has been our experience that the 12VDC pumps
when run continuously only have a life span of from 500 to
1000 hours and therefore are a frequent headache. The prototype
PAE designed and built monel keel cooler is on the supply
side of the oil loop and therefore passively cools the Naiad
oil whenever the engine is running. Unfortunately, we have
learned that our Mk 1 design of the hydraulic oil cooler is
not sufficient in performance, so we have developed a larger
and more efficient MkII version for testing on a future N40.